Drilling muds



M. R. ANNIS DRILLING MUDS Sept. 27, 1966 5 Sheets-Sheet 1 Filed Dec. 27, 1962 SATURATED A-CALCIUM SULFATE i W 1 m H W V m o a a m 2 O. 0.

zmzufilwoo @2357; 232322 PER CENT BARITES FIG- TIME, MINUTES INVENTOR.

MAX R. ANNIS,

BY XM ATTORNEY- M. R. ANNIS DRILLING MUDS Sept. 27, 1966 5 SheetsSheet 2 Filed Dec. 27, 1962 T|ME,MINUTES kzmzoilmou 922 2;

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E N R mm o N T WN u mA On O m x A M 60 80 I00 T|ME,M|NUTES FIG. 4.

8 6 4 2 0 0 O O O O M. R. ANNIS DRILLING MUDS Sept. 27, 1966 5 Sheets-Sheet 5 Filed Dec. 27, 1962 l W V W v 53:0 I :00 w z; u F m MINUTES 3 ET TIM E F' l G. 5.

INVENTOR. MAX R. A N N is BY X ATTORNEY.

United States Patent 3,275,551 DRILLING MUDS Max R. Annis, Houston, Tex., assignor, by mesne assignments, to Esso Production Research Company, Houston, Tex., a corporation of Delaware Filed Dec. 27, 1962, Ser. No. 247,594 Claims. (Cl. 2528.5)

The present invention relates to improvements in the drilling of wells and in particular, to improve drilling fluids used in rotary type we'll drilling processes. More particularly, the invention relates to drilling muds having properties 'which inhibit or prevent the sticking of drill pipe and drill collars.

In the drilling of wells by the rotary method, a drilling fluid is circulated down the drill string and up the annulus between the drill string and the borehole wall, while the drill string and drill bit attached thereto are rotated. Drilling muds used as the circulating fluid are essentially suspensions of solids in water; these solids form the bulk of the mud filter cake. In general, the solids are clays and barite and their relative amounts present in the bulk mud are controllable within limits set by the required mud density. Important functions of drilling muds are: to clean the borehole of chips and cuttings and carry these to the surface; to lubricate the drill bit and drill stem;

to form a filter cake to seal and maintain the walls of the borehole and prevent formation damage; to control the pressure on the annulus to prevent blowouts or formation breakdowns and lost returns; to sustain the cuttings in the event of rig shut down, so that these do not fall to the bottom of the hole and stick the drill pipe; and to protect the surrounding formation in order that the wellbore may thereafter be successfully surveyed by known well logging methods.

Sticking of drill pipe and drill collars during the drilling of wells is a well known problem. When drill pipe and drill collars contact the wall of the borehole, they become imbedded in the filter cake and a force is created which pushes the pipe and collars against the borehole wall. This force is equal to the product of the area per unit of length of the pipe imbedded in the filter cake, the length of the pipe imbedded, the difference between the hydrostatic drilling fluid column weight and the formation fluid pressure, and the coefficient of friction between the pipe and filter cake. This type sticking is commonly referred to as differential pressure sticking or wall sticking. Another force which causes sticking occurs for purely mechanical causes. For example, an abrupt change in direction of the borehole may cause bending of the drill pipe and the resistance to this bending may give rise to a sufiiciently large force holding the pipe against the borehole wall to cause sticking. Thus, pipe forced against the borehole wall in some manner and the resistance to movement of the pipe against the mud cake is greater than the pulling forces available which results in the pipe becoming stuck in the borehole and necessitates an expensive fishing job.

To inhibit or prevent sticking of drill pipes and drill col lars, many expedients have been tried. -It is common practice to spot oil in the well over the section where the pipe is stuck and this practice often allows the pipe to become loosened. Another practice that reduces, but does not eliminate pipe sticking is to emulsify oil in the drilling mud. To enhance the effectiveness of the oil emulsion muds in this respect, a number of special oils have been tried that are alleged to be better than the commonly used diesel oil or kerosene. Unfortunately, the majority of these special oils, other than certain kerosenes having nonfluoresc-ent properties, introduces into the circulating mud system a fluorescent material that interferes with the geologic evaluation of the formation core and cuttings samples by confusing the oil naturally in the sands with the oil of the circulating mud, and for this reason, their use is drastically restricted.

The drilling mud additive to which this invention is directed is a molybdenum complex prepared by dispersing an extract of a molybdenum compound in an oil solution of a surface active material and converting at least a portion of the molybdenum compound to the sulfide. The exact structure of the compound is unknown, but materials of this general type are found in the lubricating art to impart anti-wear properties to the lubricant.

It has been found that colloidal complexes having relatively high concentrations of molybdenum in proportion to the surfactant can be prepared by extracting an aqueous acidified solution of a molybdenum compound including molybdic acid and molybdate salts, such as ammonium molybdate, with .a volatile oil soluble solvent such as an ether or a ketone and then dispersing the solvent extract in an oil soluble surfactant. Before the solvent is removed, the dispersion is treated with a quantity of hydrogen sulfide to form molybdenum sulfide as a colloidal dispersion in the product. The complex that is formed probably contains other molybdenum compounds such as molybdenum blue and molybdenum oxides.

Among the molybdenum salts that may be used in this invention are included ammonium molybdate, sodium molybdate, potassium molybdate, barium or magnesium molybdate, and molybdates from other materials such as zinc and cadmium. Molybdi-c acid may also be used as well as molybdenum trioxide. The latter may be employed by dissolving it in an aqueous ammonia followed by treatment with hydrochloric acid. In essence, the molybdenum trioxide is first converted to ammonium molybdate.

The general procedure to be followed in preparing the additive is as follows. The molybdate is dissolved in the minimum amount of water necessary for complete solution, although the amount of water may range from 4 to 10 parts by weight per part of molybdate. Then sufiicient mineral acid such as aqueous HCl is added to furnish a solution having a normality in the range of 2 to 12 and preferably 4 to 8. Alternately, and preferably, the molybdate is dissolved in a previously prepared wateracid mixture. If the acidity is greater than 8 normal, there is a tendency for excess chlorine to appear in the product when CHl is used, while if it is below 4 normal, the molybdenum utilization, i.e., the proportion of molybdenum in the product to the molybdenum used ,in the process tends to be poor. The solution is then extracted with a volatile oil soluble solvent, e.g., a ketone or ether. After a period of agitation for proper contact with the solvent and then a period of settling for separation, the solvent extract layer is added to a suitable surfactant. Contacting temperatures and mixing rates are controlled so as to prevent foaming problems. Following the surfactant contacting step, the mixture of solvent extract and surfactant is treated by blowing through it a stream of hydrogen sulfide at a temperature in the range of 50 to F. for a sufiicient time to convert at least some of the molybdenum to the sulfide. Thereafter, the solvent and unreacted H 5 as well as any water that is present are removed by heating and by purging with an inert gas. Nitrogen is a suitable inert gas for this purpose. The final stripping temperature will depend somewhat on the ketone or ether and may reach 400 F.

Ether extraction of the acidic solution of the molybdate is preferably conducted with ethyl ether; however, other ethers may be used. For example, tetrahydrofuran can be employed when it is mixed with hexane to decrease its water solubility. Other ethers which are at least partially insoluble in water or which can be extracted from water are also useful.

The ketones used must be water-insoluble; be capable of extracting the molybdenum from the acidified aqueous solution; be compatible with the oil soluble surfactant; and not deposit molybdenum sulfide from solution when the mixture of extract and surfactant is treated with H 8. Ketones of at least 4 carbon atoms are satisfactory and ketones having as many as 10 carbons may be used. Particularly useful ones include methyl isobutyl ketone, methyl isoamyl ketone, and methyl hexyl ketone. Mixtures of such ketones may be used.

The surfactant used should have sufiicient alkalinity and should be used in a sufi'icient quantity to neutralize the free acid in the solvent extract. Also, the surfactant should be oil soluble. The ratio of surfactant to molybdenum will depend largely on the basicity of the surfactant. Surfactants that can be used include metal sulfonates, metal carbonate sols, and reaction products of metal oxides and/or hydroxides with phosphosulfurized hydrocarbons.

The sulfonates used as surfactants are the oil-soluble alkaline earth metal salts of high molecular weight sulfonic acids obtained by the sulfonation of either natural or synthetic hydrocarbons. Sulfonic acids can be prepared by treat-ing lubricating base stocks with concentrated or fuming sulfuric acid in a conventional manner to produce oil soluble mahogany acids. These sulfonic acids generally have molecular weights in the range of about 300 to 700. Petroleum sulfonates are well known in the art. Suitable sulfonic acids can also be produced by sulfonating alkylated aromatic hydrocarbons such as benzene, toluene, and xylene alkylated with olefins of olefin polymers. For example, sulfonated didodecyl benzene ,may be used.

Specific examples of sulfonates suitable for practicing this invention include calcium petroleum sulfonate, barium petroleum sulfonate, calcium di-C alkyl benzene sulfonate, barium di-C alkyl benzene sulfonate and calcium C alkyl benzene sulfonate. The C alkyl groups can be derived from diisobutylene, the C alkyl groups can be obtained from tripropylene, and the C alkyl groups can be obtained from tetraisobutylene. It is preferred to use the so-called high alkalinity type of sulfonate, which is prepared by reacting metal base in excess of that required for simple neutralization of the sulfonic acid to form an alkaline product which can then be treated with carbon dioxide to reduce its free alkalinity and form a substantially neutral final product. It is believed that the high alkalinity sulfonates are primarily dispersions of metal carbonates in the neutral sulfonates.

The reaction iPI'OdlJCtS of phosphosulfurized hydrocarbons with alkaline earth metal oxides or hydroxides can be prepared by first treating a hydrocarbon with the phosphorus sulfide and then reacting the product with an alkaline earth hydroxide or oxide, for example, barium hydroxide, preferably in the presence of an alkyl phenol or an alkyl phenol sulfide and also preferably in the presence of carbon dioxide.

The phosphosulfurized hydrocarbons may be prepared by a reaction of a sulfide of phosphorus such as P with a suitable hydrocarbon material such as a terpene, a heavy petroleum fraction or a polyolefin, the latter having a Staudinger molecular weight in the range of 500 to about 200,000 and containing from 2 to 6 carbon atoms per olefin monomer. Particularly preferred are the polybutenes having Staudinger molecular weights in the range of about 700 to about 100,000. Preferably the phosphosulfurized hydrocarbon is prepared by reacting approximately 4 moles of the hydrocarbon base stock with 1 mole of phosphorous spentasulfide under anhydrous conditions at temperatures from about 150 to about 600 F. for from about /2 to 15 hours. The preparation 4 of phosphosulfurized hydrocarbons is more fully described in US. Patent No. 2,875,188.

While the dispersion of the solvent extract of the acidic molybdate in the oil-soluble surfactant can be carried out in the presence of the surfactant per se, it is more convenient to conduct the dispersion in an oil concentrate of the detergent or surfactant. Such concentrates usually contain from about 10 to about wt. percent, preferably 20-60 wt. percent, of the surfactant in a lubricating oil. The lubricating oil may be either a mineral oil or a synthetic oil, the latter including diesters, complex esters, polysilicones, polyglycols and the like.

An example of the manner of preparation of the molybdenum complexes is as follows. One part by weight of ammonium molybdate is mixed with 6 parts of 6-normal hydrogen chloride. This solution is cooled to about 50 to 80 F. and extracted with solvent, e.g., 21.5 parts of ethyl ether or 10 parts of ketone. Separation into two layers is permitted and the extract layer is removed and stirred into 5 to 8 parts by weight of a surfactant. The dispersion is then treated with preferably one atom of sulphur per one atom of molybdenum. The amount of H 8 will depend on the amount of sulphur desired in the product which may vary from less than one weight percent to 4.5 wt. percent or more in the additive concentrate. After the H 5 treatment, the dispersion is heated and stripped with an inert gas, such as nitrogen, to remove the solvent, water, and excess H 8 and the product is filtered.

The colloidal molybdenum complex prepared by ether extraction is described in detail in US. patent application Serial No. 131,723, filed August 16, 1961, now abandoned by Elmer B. Cyphers et al., entitled Preparation of Colloidal Molybdenum Complexes. The colloidal molybdenum complex prepared by ketone extraction is described in detail in US. patent application Serial No. 157,858, filed December 7, 1961, by John A. Price, entitled Colloidal Molybdenum Complexes Prepared by Ketone Extraction, now US. Patent No. 3,140,997, Numerous examples are given in these applications for the preparation of this material.

A primary object of the present invention is to provide an improved drilling process that inhibits or prevents drill pipe and drill collar sticking. Another object of the present invention resides in providing an improved additive designed to reduce or prevent such drill pipe sticking. These additives exhibit a particularly advantageous characteristic in that no fluorescence is imparted to the drilling muds when they are used with readily available non-fluorescent kerosenes.

The above objects and other objects and advantages of the invention will be apparent from the following, more detailed description thereof when taken in conjunction with the drawings in which: I

FIG. 1 is a plot of sticking coefficient vs. percent barites for a particular mud composition;

FIGS. 2, 3, and 4 are plots of sticking coeflicients vs. set times for various drilling mud compositions; and

FIG. 5 illustrates plots of sticking coefiicients vs. set times for particular field tested drilling muds.

To evaluate the effectiveness of drilling mud additives in decreasing the tendency for drill pipe to stick, a test was devised to measure the sticking coefiicient which is defined for purposes herein as the ratio of the pulling force to the perpendicular force at the time of the measurement. Essentially, the sticking coefficient is a measure of how strongly pipe becomes stuck in the presence of a given mud system after a certain residence time under a specified perpendicular force.

The sticking coefiicient is defined for purposes herein as the tangential force required to move a plate over the mud filter cake divided by the force normal to the plate. This may be expressed as:

Thus, the sticking coefficient is a dimensionless quantity corresponding to a coefficient of friction; however, unlike a coefficient of friction it is not a constant, but is time dependent and dependent on the thickness and composition of the filter cake as well. Consequently, a single determination is not suflicient to define a sticking coefficient; instead, a curve must be determined from which the significance of the sticking coefficient may be deduced. By testing at constant filter cake thickness only, time and composition remain as the major variables.

It is known from the art that an angular, nonhydratable particle is most likely to increase the coefficient. Such a particle would be represented by the barites used to increase the density of a mud. Accordingly, two base muds were prepared containing 3.4% by volume of bentonite clay. One was of fresh water and the other was saturated with calcium sulfate by the addition of 4 lbs. per barrel of that material. Each mud was weighted with barites in amounts from to 27% by volume to give muds that weigh from about 8.5 to 17 lbs. per gallon. Curves for the sticking coefficient vs. time were run on each of these muds and it was noted in each case that the sticking coefiicient increased rapidly with time during the first 10 to 40 minutes and became substantially level at a constant maximum value. This maximum value for sticking coefficient is shown as a function of barites concentration in FIG. 1. These data show the maximum sticking coefficient is a function of the barites concentration. The break in curve A at 16% barites reflects a change in the nature of the filter cake when the compressibility of the cake becomes more controlled by the barites than by the bentonite. This means that sticking associated with the pressure differential is most likely to occur in the deep, high pressure wells where high density muds are needed and the expense of fishing is the greatest.

The sticking coefficient was experimentally determined for drilling muds of various compositions using the following technique:

A Berea sandstone core 2" in diameter by 1" thick was mounted in a pressure vessel having a removable cap and packing box, and through the side of which a piston was run to attach a 2%" by 2%" flat steel plate to an hydraulic piston. A gauge was attached to the cap to measure the pressure differential across the core and another gauge Was attached to the hydraulic cylinder to measure the force required to move the flat test plate. The test mud was placed in the pressure vessel and filtration was conducted at pressures of 500 p.s.i. until a filter cake was built up. To make each test comparable, the filtration was performed so that a filter cake of the same thickness was obtained for each test. The flat test plate was placed on the filter cake and 500 p.s.i. pressure was applied on the mud to force the plate against the filter cake. The force required to just initiate movement of the plate was measured with the hydraulic cylinder. The measurements could be made step wise at different time intervals with the same result as when the system remained undisturbed for the total time and by making such step wise measurements at different times a curve of sticking coefficient as a function of time could be drawn for a particular mud.

It was found that the molybdenum complexes described supra must be used with oil in the mud to be effective in reducing the sticking coefficient. Accordingly the tests were made with about 10% oil emulsified in the mud. In practice, the compounds may be used in muds containing oil in amounts normally encountered in field practice, i.e., 5 to 20%. The amount of the additive used in the experiments is expressed as percent by volume of the oil in the mud and it would remain the same throughout the range of concentrations of oil in the mud.

Tests conducted with additives of different compositions showed that for best results both molybdenum and sulphur must be present inthe complex.

A typical base mud is one composed of about 14 lbs. bentonite clay (Aquagel), 30 lbs. low yield clay (Xact Clay), 4.5 lbs. ferrochromlignosulfonate (Q-Broxin), 0.5 'lb. sodium hydroxide, 8 lbs. calcium sulfate, and barites to give a weight of the final mud of 15.5 lbs. .per gal. These ingredients are expressed as lbs. per barrel of water. This composition makes more than a barrel of total mud. The results of tests with a mud of this particular composition are shown in FIG. 2 on which curves are plotted for the base mud without oil emulsified in it, dotted line curve B, for the base mud with 10% nonfluorescent kerosene emulsified therein, curve C, and for the emulsion mud with the complex added in the amount of two vol. percent of the oil phase, curve D.

Curve B of FIG. 2 shows a sticking coefficient of about 0.247 after 20 minutes, which increased to only 0.250 after 3 hours. This indicates that with this mud the time that the pipe could remain quiescent would be quite short if sticking is to be avoided. It is also seen in FIG. 2 that the addition of the complex, curve D, contributed significantly to the non-sticking quality of the mud when compared with the oil emulsion mud, curve C. To emphasize the significance of the differences, assume sticking coefficients of 0.08, 0.10, and 0.12 and note the times available for each of the three muds, curves B, C, and D, before that particular coefficient is reached. First, with 0.08, it is seen that this value is reached in about 7 minutes with the base mud, curve B; about 13 minutes with the emulsion mud, curve C; and about 20' minutes with the additive mud, curve D. Second, with 0.10 the times become, respectively, 8 minutes, 22 minutes, and 40 minutes. Third, when the coefficient is 0.12, the times be.- come 10 minutes, 50 minutes, and more than minutes, respectively. In many cases, this difference between 13 and 20 minutes or between 22 and 40.minutes, or between 50 and 120 minutes could be very significant in avoiding sticking of the drill pipe. It is seen from these curves that if sticking coefficients above 0.14 can be tolerated, then a long time could elapse before'the pipe would stick with either the emulsion mud, curve C, or the treated emulsion mud, curve D; but there would still be a decided advantage in the use of the treated emulsion mud. The real significance of the difference between the emulsion mud and the treated emulsion mud is better appreciated when it is noted that emulsion muds help, but do not alleviate the problem of differential sticking. Thus, the treatment of the mud with the additive complex, which about doubles the time available before reaching any particular sticking coefficient, is quite advantageous.

The results illustrated in FIG. 3 show that molybdenum decreased the sticking coefficient during the early periods of the test and that sulphur was effective in the later periods. When both were present, the sticking coefiicient was reduced throughout the entire test period.

Included in FIG. 3 are the results obtained with molybdenum disulfide, a commercial lubricant sold under the trade name of Molykote, dotted line curve F, which indicates that the oil soluble surfactant of the complex also contributes to the effectiveness of the material. It is seen that Molykote raised the coefficient at short set times, but gave some lowering after two hours when compared with the base mud, curve E. In this figure also, curve G designates a material that is a reaction product of ammonium molybdate and octylene glycol and contains no sulphur. Curve H of FIG. 3 represents the results of using test material as an additive which is a reaction product of 780 molecular weight polybutylene with 24% phosphorous pentasulfide and contains no molybdenum. Curve J represents the results of tests using the complex of the invention as an additive.

An additional series of tests were made to which concentrations of the additive of 0.1, 0.2, 0.4, and 1.0% by volume of the oil in the mud were added to investigate the effect of concentration of the additive in the emulsion mud. The results of these measurements of the sticking coeflicients with time are illustrated by the curves of FIG. 4. It is seen from these curves (note the curve for 0.1% is omitted, but it falls between those of the base mud curve K and the 0.2% concentration curve L) that the addition of 0.4% of this complex was about as effective as the addition of 1% of the additive, see curve M. From this it is seen that the material added in the range of from 0.1% to 1.0% would be suflicient with a preferred range from 0.2 to 0.5% by volume of oil in the mud; in field practice as much as 5% may be used.

An additive or complex of the invention was field tested in a well while drilling from approximately 12,500 feet to 13,500 feet. Twenty-five gallons of this additive were added to a mud composed of a 12.6 lbs. per gallon gyp-Q-Broxin mud containing 8% kerosene and 24% solids, and having a funnel viscosity of 50 seconds and an API filtration of 5.2 ml. The 25 gallons were added over one circulation cycle. Sticking coefficients and flow properties tests were performed after the muds containing the additive had completed 1 and 3 circulations and again on a sample circulated from the bottom of the hole after a round trip. Twenty-four hours after adding the first 25 gallons of additive, another 65 gallons were added and tests were conducted periodically over the next three days.

Data illustrating the effect of this additive on sticking coeflicient are shown in FIG. 5. The sticking coefiicient measured on the first circulation after adding the additive showed a decrease in the 60-minute set time value of about 10%, see curves N and 0. After three circulations, the 60-minute sticking coefficient had decreased an additional 5%, compare curves and P, and remained at this point, about 15% below that of the base mud, until 65 more gallons of complex were added. The initial 25 gallons of additive represented about 0.3 volume percent of the kerosene in the mud and was, therefore, still below that necessary to give the full reduction in sticking coefficient to be expected. The 65 gallons added next brought the concentration up to approximately 1.0% of kerosene concentration or to what is considered a suitable amount to achieve the full reduction in sticking coeflicient.

The second addition of this additive caused reductions in the sticking coelficient in the mud very similar to the first, as seen in curves Q and R. On the first circulation, the 60-minute sticking coefficient was further decreased about 10% and on the third circulation, it was decreased an additional (not shown). The sticking coefficient remained at this point, about 25 or 30% below that of the base mud, curve N, during the duration of the test. The greater reduction in the sticking coefiicient in the field test versus that in the laboratory test may be attributable to better mixing in the field test. The continuance in the drop in the sticking coefficient between the first and third circulations suggest that better mixing is the factor that provides better field results.

As mentioned previously, the force required to free the drilling collars depends on the length exposed to a permeable formation, the area of the pipe embedded, the pressure differential, and the coeflicient of friction between the pipe and the embedding material. All of these factors vary drastically not only from well to well, but from point to point within the given well. The length will vary because the ratio of permeable to impermeable formations exposed over the length of the drill collars changes constantly, e.g., from 0 when a thick bed of shale is being drilled to a theoretical 100% when a thick sand is drilled. Also controlling the length exposed to imbedment is the extent of the washed out places compared with the amount of hole remaining in gauge. The pressure difierential increases with depth at constant mud weight and also the mud weight often is varied, usually becoming more dense with greater depth. In addition,

the coeflicient of friction changes with the mud composition, especially as has been shown when barites has been added to increase the Weight or when excessive amounts of sand are suspended in the mud. Consequently, it is difficult to attach any absolute value to the sticking coefficient; that is, to state that a mud with a coefficient of 0.15 is satisfactory, but one above 0.15 is not suitable. The benefits to be derived from decreasing the sticking coefficient are illustrated in the following example. Investigators have found a sticking force of 42 lbs. per foot of pipe for each p.s.i. differential when the coeflicient of friction is one. This value is based on 7" drill collars in 8% hole with a filter cake A1" thick-conditions that are not unrealistic in well drilling. Using this calculation and assuming 200 p.s.i. pressure differential with feet of drill collars involved in the sticking, it is seen that the total force required to pull the pipe loose would be:

1 42 200 100=840,000 lbs.

Using 5 inch 19.5 lbs. per foot drill pipe which has a yield strength of 395,000 lbs. in tension at 10,000 feet, there would be a hook load of about 175,000 lbs. This would leave but 220,000 lbs. pull allowable before the pipe parted. Thus, with the pipe stuck under these conditions, it would be impossible to pull the pipe and an additional pull of 620,000 lbs. would be needed or some other action would have to be taken. The logical action is to reduce the coefficient of friction or the mud weight. Well conditions often dictate that mud weight cannot be reduced, which usually means that the coefficient of friction must be reduced. Employing the above assumptions, the coefficient to permit freeing of the drill pipe with not more than the allowable 220,000 lbs. pull available can be calculated as follows:

This represents the maximum coeflicient and some allowance for safety would be made in actual practice. Under these conditions the mud used in FIG. 2, curve B, would be adequate, even without oil emulsified therein, since the coeflicient even after a long time of setting was 0.250.

In this same system with a pressure differential of 400 p.s.i., a figure which is within normal field practice, a coeflicient of 0.13 would be needed as derived below:

Assuming this is the mud illustrated in FIG. 2, it is seen that with a sticking coeflicient of 0.13, sticking might occur in the base mud, curve B, after about 10 minutes. In the base mud with oil emulsified therein, curve C, about 80 minutes would be available and with the treated mud, curve D, the time would exceed minutes. Under these conditions it could be concluded that with the base mud sticking would be probable, and with the emulsion mud, it would be possible; but with the treated emulsion mud, it would be highly unlikely that the pipe would become stuck. This example illustrates the significance of the benefit derived from the use of the treating agent in an oil emulsion mud.

Any oil suitable to emulsify in a mud may be used, provided the fluorescence of the oil is not objectionable. Nonfluorescent oils used in conjunction with the complex additives of the invention give a mud with superior properties and which is not fluorescent.

Having fully described the nature, operation, objects, and advantages of my invention, I claim:

1. 'In a well-drilling process in which a drilling fluid containing an oil in water emulsion is circulated down the drill string and up the annulus between the drill string and the bore hole wall, the improvement comprising adding to said drilling fluid in amounts sufficient to inhibit sticking of drill pipe and drill collars a colloidal complex containing molybdenum prepared by extracting an acidic aqueous solution of a molybdenum compound selected from the group consisting of molybdic acid, ammonium salts of molybdic acid, and metal salts of molybdic acid, with a volatile oil-soluble solvent selected from the group consisting of ethers that are extractable from water and ketones having in the range of 4 to carbon atoms, said acidic solution having been acidified with a mineral acid to an acidity within the range of 2 N to 12 N, dispersing the resultant oil-soluble solvent extract in an oil-soluble basic metal-containing dispersant having suflicient alkalinity to neutralize the free acidity of said extract, treating said dispersion with hydrogen sulfide and then removing the oil-soluble solvent from the dispersion.

2. A process as defined by claim 1 in which said dispersion is treated with hydrogen sulfide by blowing H 6 through the dispersion.

3. A process as defined by claim 1 wherein said aqueous solution is acidified with *HCl and has an acidity in the range from 4 N to 8 N.

4. A process as defined in claim 1 wherein said dispersant comprises a high-alkalinity metal salt of a hydrocarbon sulfonic acid having a molecular weight in the range of 300 to 700.

5. A process as defined by claim 1 wherein said dispersant comprises the reaction product of a phosphosulfurized hydrocarbon with a basic substance selected from the group consisting of alkaline earth metal oxides and alkaline earth metal hydroxides.

6. A drilling mud containing an oil in water emulsion and sufficient amounts of a colloidal complex containing molybdenum, to inhibit sticking of drill pipe and drill collars, said colloidal complex being prepared by extracting an acidic aqueous solution of a molybdenum compound selected from the group consisting of molybdic acid, ammonium salts of molybdic acid, and metal salts of molybdic acid with a volatile oil-soluble solvent selected from the group consisting of ethers that are extractable from water and ketones having in the range of 4 to 10 carbon atoms, said acidic solution having been acidified with a mineral acid to an acidity within the range of 2 N to 12 N, dispersing the resultant oil-soluble solvent extract in an oil-soluble basic metal-containing dispersant having sufiicient alkalinity to neutralize the free acidity of said extract, treating said dispersion with hydrogen sulfide and then removing the oil-soluble solvent from the dispersion.

7. A drilling mud as defined in claim 6 in which said dispersion is treated with hydrogen sulfide by blowing H 8 through the dispersion.

8. A drilling mud as defined in claim 6 wherein said aqueous solution is acidified with HCl and has an acidity in the range from 4 N to 8 N.

9. A drilling mud as defined in claim 6 wherein said dispersant comprises a high-alkalinity metal salt of a hydrocarbon sulfonic acid having a molecular weight in the range of 300 to 700.

10. A drilling mud as defined in claim 6 wherein said dispersant comprises the reaction product of a phosphosulfur-ized hydrocarbon with a basic substance selected from the group consisting of alkaline earth metal oxides and alkaline earth metal hydroxides.

References Cited by the Examiner UNITED STATES PATENTS 2,805,991 9/ 1957 Tailleur 252-8.5 2,987,478 6/ 1961 *Matson 2-5246. 1 3,047,494 7/1962 Browning 252 8.5 3,140,997 7/1964 Price 252-33 OTHER REFERENCES Helmick et al.: Pressure-Differential Sticking of Drill Pipe, Article in the Oil and Gas Journal, June 17, 1957, pages 132 to 13 6.

LEON 'D. ROSDOL, Primary Examiner.

H. B. GUY NN, Assistant Examiner. 

6. A DRILLING MUD CONTAINING AN OIL IN WATER EMULSION AND SUFFICIENT AMOUNTS OF A COLLOIDAL COMPLEX CONTAINING MOLYBDENUM, TO INHIBIT STICKING OF DRILL PIPE AND DRILL COLLARS, SAID COLLOIDAL COMPLEX BEING PREPARED BY EXTRACTING AN ACIDIC AQUEOUS SOLUTION OF A MOLYBDENUM COMPOUND SELECTED FROM THE GROUP CONSISTING OF MOLYBDIC ACID, AMMONIUM SALTS OF MOLYBDIC ACID, AND METAL SALTS OF MOLYBDIC ACID WITH A VOLATILE OIL-SOLUBLE SOLVENT SELECTED FROM THE GROUP CONSISTING OF ETHERS THAT ARE EXTRACTABLE FROM WATER AND KETONES HAVING IN THE RANGE OF 4 TO 10 CARBON ATOMS, SAID ACIDIC SOLUTION HAVING BEEN ACIDIFIED WITH A MINERAL ACID TO AN ACIDITY WITHIN THE RANGE OF 2 N TO 12 N, DISPERSING THE RESULTANT OIL-SOLUBLE SOLVENT EXTRACT IN AN OIL-SOLUBLE BASIC METAL-CONTAINING DISPERSANT HAVING SUFFICIENT ALKALINITY TO NEUTRALIZE THE FREE ACIDITY OF SAID EXTRACT, TREATING SAID DISPERSION WITH HYDROGEN SULFIDE AND THEN REMOVING THE OIL-SOLUBLE SOLVENT FROM THE DISPERSION. 